Optical properties of the NGC 5328 group of galaxies

We present the results of a photometric and spectroscopic study of seven members of the NGC 5328 group of galaxies, a chain of galaxies spanning over 200 kpc (H_0 = 70 km/s/Mpc). We analyze the galaxy structure and study the emission line properties of the group members looking for signatures of star formation and AGN activity. We finally attempt to infer, from the modeling of line-strength indices, the stellar population ages of the early-type members. We investigate also the presence of a dwarf galaxy population associated with the bright members. The group is composed of a large fraction of early-type galaxies including NGC 5328 and NGC 5330, two bona fide ellipticals at the center of the group. In both galaxies no recent star formation episodes are detected by the H_beta vs. MgFe indices of these galaxies. 2MASX J13524838-2829584 has extremely boxy isophotes which are believed to be connected to a merging event: line strength indices suggest that this object probably had a recent star formation episode. A warped disc component emerges from the model subtracted image of 2MASX J13530016-2827061 which is interpreted as a signature of an ongoing interaction with the rest of the group. Ongoing star formation and nuclear activity is present in the projected outskirts of the group. The two early-type galaxies 2MASX J13523852-2830444 and 2MASX J13525393-2831421 show spectral signatures of star formation, while a Seyfert 2 type nuclear activity is detected in MCG -5-33-29.Comment: 18 pages, 12 figures, accepted for publication in MNRA

Prevention of neurological injuries during mandibular third molar surgery: technical notes

Surgery to the mandibular third molar is common, and injuries to the inferior alveolar nerve and the lingual nerve are well-recognized complications of this procedure. The aim of these technical notes is to describe operative measures for reducing neurological complications during mandibular third molar surgery. The following procedure should be used to prevent damage to the inferior alveolar nerve: a well-designed mucoperiosteal flap, to obtain appropriate access to the surgical area; a conservative ostectomy on the distal and distal-lingual side; tooth sectioning, to facilitate its removal by decreasing the retention zones; tooth dislocation in the path of withdrawal imposed by the curvature of the root apex; and careful socket debridement, when the roots of the extracted tooth are in intimate contact with the mandibular canal. To prevent injury to the lingual nerve, it is important (I) to assess the integrity of the mandibular inner cortex and exclude the presence of fenestration, which could cause the dislocation of the tooth or its fragment into the sublingual or submandibular space; (II) to avoid inappropriate or excessive dislocation proceedings, in order to prevent lingual cortex fracture; (III) to perform horizontal mesial-distal crown sectioning of the lingually inclined tooth; (IV) to protect the lingual flap with a retractor showing the cortical ridge; and (V) to pass the suture not too apically and from the inner side in a buccal-lingual direction in the retromolar are

The cluster population of the irregular galaxy NGC 4449 as seen by the Hubble Advanced Camera for Surveys

We present a study of the star cluster population in the starburst irregular galaxy NGC 4449 based on B, V, I, and Ha images taken with the Advanced Camera for Surveys on the Hubble Space Telescope. We derive the cluster properties such as size, ellipticity, and total magnitudes. Cluster ages and masses are derived fitting the observed spectral energy distributions with different population synthesis models. Our analysis is strongly affected by the age-metallicity degeneracy; however, if we assume a metallicity of ~1/4 solar, as derived from spectroscopy of HII regions, we find that the clusters have ages distributed quite continuously over a Hubble time, and they have masses from ~10^3 M_sun up to ~2 x 10^6 M_sun, assuming a Salpeters' IMF down to 0.1 M_sun. Young clusters are preferentially located in regions of young star formation, while old clusters are distributed over the whole NGC 4449 field of view, like the old stars (although we notice that some old clusters follow linear structures, possibly a reflection of past satellite accretion). The high SF activity in NGC 4449 is confirmed by its specific frequency of young massive clusters, higher than the average value found in nearby spirals and in the LMC (but lower than in other starburst dwarfs such as NGC 1705 and NGC 1569), and by the flat slope of the cluster luminosity function (dN(L_V)\propto L_V^{-1.5} dL for clusters younger than 1 Gyr). We use the upper envelope of the cluster log(mass) versus log(age) distribution to quantify cluster disruption, and do not find evidence for the high (90%) long-term infant mortality found by some studies. For the red clusters, we find correlations between size, ellipticity, luminosity and mass: brighter and more massive clusters tend to be more compact, and brighter clusters tend to be also more elliptical.Comment: Accepted for publication on AJ, one data point changed in Fig. 1

Nearby early-type galaxies with ionized gas.II. Line-strength indices for 18 additional galaxies

Rampazzo et al. 2005 (Paper I) presented a data-set of line-strength indices for 50 early-type galaxies in the nearby Universe. The galaxy sample is biased toward galaxies showing emission lines, located in environments corresponding to a broad range of local galaxy densities, although predominantly in low density environments. The present addendum to Paper I enlarges the above data-set of line-strength indices by analyzing 18 additional early-type galaxies (three galaxies, namely NGC 3607, NGC 5077 and NGC 5898 have been already presented in the previous set). As in Paper I, we measured 25 line-strength indices, defined by the Lick IDS "standard" system (Trager et al. 1998; Worthey & Ottaviani 1997), for 7 luminosity weighted apertures and 4 gradients of each galaxy. This paper presents the line-strength data-set and compares it with the available data in the literature.Comment: 18 pages, A&A in pres

The Star Formation History of NGC 1705: a Post-Starburst Galaxy on the Verge of Activity

We infer the star formation history in different regions of the blue compact dwarf NGC 1705 by comparing synthetic color-magnitude diagrams with HST optical and near-infrared photometry. We find that NGC 1705 is not a young galaxy because its star formation commenced at least 5 Gyr ago. On the other hand, we confirm the existence of a recent burst of star formation between 15 and 10 Myr ago. We also find evidence for new strong activity, which started 3 Myr ago and is still continuing. The old population is spread across the entire galaxy, while the young and intermediate stars are more concentrated in the central regions. We derive an almost continuous star formation with variable rate, and exclude the presence of long quiescent phases between the episodes during the last ~1 Gyr. The central regions experienced an episode of star formation of \~0.07 Msun/yr (for a Salpeter initial mass function [IMF]) 15 to 10 Myr ago. This coincides with the strong activity in the central super star cluster. We find a rate of ~0.3 Msun/yr for the youngest ongoing burst which started ~3 Myr ago. This is higher than in other dwarfs and comparable to the rate of NGC 1569. The star formation rate of earlier episodes is not especially high and falls in the range 10^{-3}-10^{-1} Msun/yr. The IMF is close to the Salpeter value or slightly steeper.Comment: 34 pages, including 6 tables and 14 .ps figures (9 in colour), AJ in pres

An off-centred bulge or a satellite? Hydrodynamical N-body simulations of the disc galaxy NGC 5474

We present dynamical models of the star-forming galaxy NGC 5474 based on N-body hydrodynamical numerical simulations. We investigate the possible origin of the compact round stellar structure, generally interpreted as the bulge of the galaxy, but unusually off-set by ≃ 1 kpc in projection from the visual and the kinematic centres of both the star and the gas discs. We argue that it is very unlikely that the putative bulge is in a coplanar orbit in the disc plane, showing that such a configuration would be hardly compatible with its smooth and regular spatial distribution, and, in case its mass is above 108 M⊙, also with the regular H I velocity field of NGC 5474. Instead, if the putative bulge is in fact an early-type satellite galaxy orbiting around NGC 5474, not only the off-set can be easily produced by projection effects, but our simulations suggest that the gravitational interaction between the two systems can explain also the warped H I distribution of NGC 5474 and the formation of its loose spiral arms. As a by-product of the simulations, we find that the peculiar overdensity of old stars detected in the south-west region of NGC 5474 may be explained with the interaction between NGC 5474 and a smaller stellar system, unrelated to the putative bulge, accreted in the disc plane

Emission lines in early-type galaxies: active nuclei or stars?

We selected 27244 nearby, red, giant early-type galaxies (RGEs) from the Sloan Digital Sky Survey (SDSS). In a large fraction (53%) of their spectra the [O III] emission line is detected, with an equivalent width (EW) distribution strongly clustered around ~0.75 A. The vast majority of those RGEs for which it is possible to derive emission line ratios (amounting to about half of the sample) show values characteristic of LINERs. The close connection between emission lines and stellar continuum points to stellar processes as the most likely source of the bulk of the ionizing photons in RGEs, rather than active nuclei. In particular, the observed EW and optical line ratios are consistent with the predictions of models in which the photoionization comes from to hot evolved stars. Shocks driven by supernovae or stellar ejecta might also contribute to the ionization budget. A minority, ~4%, of the galaxies show emission lines with an equivalent that is width a factor of ~2 greater than the sample median. Only among them are Seyfert-like spectra found. Furthermore, 40% of this subgroup have a radio counterpart, compared to ~6% of the rest of the sample. These characteristics argue in favor of an AGN origin for their emission lines. Emission lines diagnostic diagrams do not reveal a distinction between the AGN subset and the other members of the sample, and consequently they are not a useful tool for establishing the dominant source of the ionizing photons, which is better predicted by the EW of the emission lines.Comment: Accepted for publication in A&